pinctrl: atlas7: adjust pin groups of atlas7 nanddisk

Remove write-protect and chip-selector pins from nand pin group.
And then create two separate pin groups for these two pin.

So the nand driver can choose correct pin groups as board desgin:
For example:
1. nand without wp&cs:
	nand@17050000 {
		pinctrl-0 = <&nd_df_basic_pmx>;
	};
2. nand with wp
        nand@17050000 {
                pinctrl-0 = <&nd_df_basic_pmx &nd_df_wp_pmx>;
        };
3. nand with cs:
        nand@17050000 {
                pinctrl-0 = <&nd_df_basic_pmx &nd_df_cs_pmx>;
        };
4. nand with wp&cs:
        nand@17050000 {
                pinctrl-0 = <&nd_df_basic_pmx &nd_df_wp_pmx &nd_df_cs_pmx>;
        };

Signed-off-by: Wei Chen <Wei.Chen@csr.com>
Signed-off-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>